Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $212.26   7.522%   $228.2262   $228.23   $228.25   $228.20  
  Purchase #2 $64.34   3.690%   $66.7141   $66.71   $66.70   $66.70  
  Purchase #3 $60.59   4.750%   $63.468   $63.47   $63.45   $63.50  
  Purchase #4 $232.51   11.276%   $258.7278   $258.73   $258.75   $258.70  
  Purchase #5 $209.75   3.869%   $217.8652   $217.87   $217.85   $217.90  
  Purchase #6 $56.46   7.506%   $60.6979   $60.70   $60.70   $60.70  
  Purchase #7 $227.50   10.549%   $251.499   $251.50   $251.50   $251.50  
  7 purchase totals = $1,063.41       $1,147.1982   $1,147.21   $1,147.20   $1,147.20